In the manufacture of metal strip such as steel plate and steel sheet, a heated slab of steel is passed between rollers in a rolling mill. This reduces the thickness of the slab to transform it into steel strip. Such treatment is referred to as "hot rolling" as the slab is introduced into the rolling mill in a red hot state. The finished product from the rolling mill is accordingly called "hot rolled steel" and is generally coiled for transport and further processing.
The subsequent processing of hot rolled steel may include: cold rolling to further reduce thickness; painting; galvanizing; and plating with chrome or other metals.
In view of the tendency of steel to oxidize, in particular at the high temperatures used during hot rolling, it is generally necessary to surface treat the hot rolled strip to render it suitable for subsequent processing. One method of surface treating the hot rolled steel strip is referred to as "pickling" and involves passing the strip through an acid bath to dissolve any surface oxides or impurities.
Immediately subsequent to pickling, it is necessary to rinse the steel strip to remove any remaining acid. Failure to rinse the acid from the strip will result in corrosion damage to the strip.
Thinner strip (up to 0.250" thick) may be pickled in continuous pickle lines which have a series of deflector rolls, which bend the sheet in motion in order to pass it through a rinse bath. For thicker strip, a push-pull pickle line is utilized which does not have the bending feature. In a push-pull pickle line, the strip is fed through generally horizontally and pickling and rinsing fluids are sprayed at the sheet.
Oxidation of the pickled strip is often encountered in the rinsing stages utilizing a spray type rinse system on all types of pickle lines, during line stops. Such line stops may take place according to schedule or may be inadvertent. Those portions of the strip which are exposed to air will generally commence oxidizing in approximately 30 seconds, resulting in staining of the sheet which gives rise to poor adhesion of paint or plating materials, and cosmetic surface blemishes. Furthermore, although the use of a spray system avoids having to bend heavier gauge metal strip, the spraying of rinse fluid results in air entrainment in the rinse fluid.
An object of the present invention is to provide a rinse system for all types of pickling lines, that will tolerate longer line shutdowns than that taking place in conventional spray systems, without oxidation of the strip surface.
It is a further object of this invention to provide a rinse system for all strip thicknesses, which avoids direct spraying of rinse fluid at the metal strip.
It is a still further object of the present invention to provide a rinse system which is efficient in the use of rinse fluids in order to minimize the fresh fluid requirement.